Recent advances in imaging biological cells using optical tomography have been developed by Nelson as disclosed, for example, in U.S. Pat. No. 8,522,775, issued Feb. 18, 2003, and entitled “APPARATUS AND METHOD FOR IMAGING SMALL OBJECTS IN A FLOW STREAM USING OPTICAL TOMOGRAPHY,” the full disclosure of which is incorporated by reference. Further development in the field is taught in Fauver et al., U.S. patent application Ser. No. 10/716,744, filed Nov. 18, 2003 and published as US Publication No. US-2004-0076319-A1 on Apr. 22, 2004, entitled “METHOD AND APPARATUS OF SHADOWGRAM FORMATION FOR OPTICAL TOMOGRAPHY,” the full disclosure of which is also incorporated by reference.
Processing in such an optical tomography system begins with specimen preparation. Typically, specimens taken from a patient are received from a hospital or clinic and processed to remove non-diagnostic elements, fixed and then stained. Stained specimens are mixed with an optical gel and inserted into a microcapillary tube. Images of objects in the specimen, such as cells, are produced using an optical tomography system. When acquired using extended depth of field optical techniques, the resultant projection images may comprise a set of extended depth of field images from differing perspectives called “pseudo-projection images.”
The set of projection images can be reconstructed using backprojection and filtering techniques to yield a reconstructed 3D image of a cell of interest. The most common and easily implemented reconstruction algorithms, known as filtered backprojection methods, are derived from a similar algorithm in x-ray computed tomography (CT) using parallel-beam geometry. (See the following references, for example, Kak, A. C. and Slaney, M., Principles of Computerized Tomographic Imaging, IEEE Press, New York, 1988, and Herman, G., Image Reconstruction from Projections: The Fundamentals of Computerized Tomography, Academic Press, New York, 1980). These methods are based on theorems for Radon transforms with modifications that reflect the particular geometry of the source/detector configuration and the ray paths in the irradiating beam.
Unfortunately, known techniques do not adequately address several error mechanisms that may be introduced during the acquisition of projection images, including pseudo-projection images. Such acquisition errors may adversely affect post acquisition reconstruction of multi-dimensional images. Errors may be introduced, for example, by mechanical misalignments causing centering errors, by light transmission effects described by Beer's law, by characteristics of optical transfer functions inherent in a set of optics, and by distortions caused by undesirable lens effects at material interfaces such as tube walls.
Adequate solutions to the above-identified error mechanisms are lacking. Further, known techniques for developing filters lack a method for developing optimized filters for backprojection of pseudo-projection images. As a result there is a need for systems and methods for mitigating such errors and their resultant adverse effects and for developing optimized filters.